This invention relates to an internal-combustion engine including at least two cylinder groups or cylinders to which one separate exhaust gas pipe respectively is assigned which has a catalytic emission control system and which is a component of an exhaust gas system. The internal-combustion engine further includes a device for shutting-off a cylinder group by preventing the fuel supply while the charge cycle of this cylinder group is maintained. The term "cylinder group" is to also explicitly include a single cylinder when a separate exhaust gas pipe with an individual, so-called exhaust gas catalyst, is assigned to it.
An internal-combustion engine, such as is known from German Patent document DE-OS 22 42 899, has the disadvantage that the catalytic emission control system of the cylinder group which can be shut-off will cool when this cylinder group is shut off. Furthermore, a charge cycle takes place in this shut-off cylinder group; that is, fresh gas is charged into the combustion spaces of the cylinders, is compressed, and is pushed out again. For reasons of simplicity, the cylinder shut-off does not take place by stopping some control elements/charge cycle valves for the load change but only by means of preventing the supply of fuel to the combustion spaces or cylinders of the shut-off cylinder group.
On the other hand, catalytic emission control systems (exhaust gas catalysts) require a certain operating temperature above which they become capable of converting harmful exhaust gas constituents. When a cylinder group is shut-off, a gas flow continues to pass through the assigned exhaust gas catalyst. This results in its cooling since this gas flow was naturally not significantly heated in the unfired cylinders. In this case, it is possible that the temperature of the exhaust gas catalyst may fall below its operating temperature. When subsequently the previously shut-off cylinder group is again connected; that is, subsequently not only fresh gas but fuel is fed to this cylinder group, then its exhaust gas catalyst will at first not be able to convert the pollutants of the exhaust gas but must first be brought to its operating temperature by means of the then hot exhaust gases.
There are therefore needed measures by which a cooling of the catalytic emission control device of the shut-off cylinder group can be avoided.
These needs are met by constructing the whole exhaust system in such a manner that the gases emitted from the shut-off cylinder group are heated by the exhaust gases of the continuously fired cylinder group.
It is an advantage of the present invention that the exhaust gas of the fired cylinder group of the catalytic emission control system is supplied to the shut-off cylinder group.
It is a further advantage of the present invention that the catalytic emission control system of the shut-off cylinder group has at least two monoliths arranged in series. The exhaust gases of the fired cylinder group are introduced downstream of the first monolith.
Yet another advantage of the present invention occurs by removing the gases emitted from the shut-off cylinder group upstream of the assigned catalytic emission control system. These removed gases are introduced into the exhaust gas pipe of the fired cylinder group.
Still yet another advantage of the present invention provides the catalytic emission control device of the fired cylinder group with at least two monoliths arranged in series. The gases emitted from the shut-off cylinder group are introduced downstream of the first monolith.
It is a further advantage of the present invention to provide the catalytic emission control system of the shut-off cylinder group with a heat-transmitting connection with the catalytic emission control system of the continuously fired cylinder group.
It is yet another further advantage of the present invention to provide one of the catalytic emission control systems with a hollow construction which envelopes the other catalytic emission control system.
A further advantage of the present invention provides for the combination of the exhaust gas pipes of the individual cylinder groups downstream of the catalytic emission control systems to form a common exhaust gas pipe.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.